Although many different types of adhesives are presently commercially available, and are found to be entirely satisfactory for their intended purposes, the demand remains for adhesive formulations capable of developing high levels of strength in brief periods of time and under a wide variety of conditions. A difficulty commonly encountered in producing certain types of fast-acting adhesives relates to the tendency for such products to cure prematurely; i.e., to have an undesirably short or unpredictable shelf-life. Thus, it is important that such a material be stable against reaction until such time as it is applied to the workpiece, and to thereupon cure quickly to produce the desired levels of bond strength. Moreover, the applicability of an adhesive to effect bonding of a wide variety of diverse materials is of obvious advantage in maximizing its utility, and hence its value in the marketplace.
While commercially available anaerobic acrylate adhesives are capable of developing excellent levels of tensile and impact strength after relatively short cure times, their use is limited, as a practical matter, to the bonding of nonporous surfaces such as of metal, glass, and the like, due to the need to exclude oxygen from the reaction situs. The same characteristic also limits the utility of anaerobic adhesives for gap filling applications, due to the tendency for oxygen to migrate to portions of the adhesive residing within gaps of more than a certain minimum spacing, thereby precluding the development of bond strength by maintaining the cure reaction reversible. Furthermore, if the gap is too wide, the adhesive will often drip upon elements that are not to be bonded, or that must be kept from foreign substances, thus producing undesirable or, indeed, intolerable consequences. Finally, the presently available anaerobic adhesives have a tendency to harden prematurely, even in the absence of any activator and despite measures to maintain an oxygen-containing atmosphere, which obviously is highly undesirable.
Accordingly, it is a primary object of the present invention to provide a novel adhesive formulation that is capable of producing high levels of bond strength in very brief cure times, and to do so under conditions that are either aerobic or anaerobic.
It is also an object of the invention to provide a method for effecting the adhesive bonding or either porous or nonporous elements in brief curing periods and under either aerobic or anaerobic conditions.
Another object of the invention is to provide such a novel composition based upon ingredients that are conventional, readily available, and not unduly expensive, and which does not set up prematurely.